1. Field of the Invention
This invention relates to a communication system and traffic control technology for computer networks connecting a plurality of server computers (hereafter simply referred to as xe2x80x9cserversxe2x80x9d) and client computers (hereafter simply referred to as xe2x80x9cclientsxe2x80x9d) and relates in particular to communication systems for dispersing the overall traffic of the network by dynamically switching the server performing client communications based on the status of traffic or vacant (idle) bandwidth of the network.
2. Description of the Prior Art
In the computer network system connecting server and client in the technology of the prior art, generally, a plurality of servers are connected for dispersing the communications load and preventing impediments to operation. In such cases, service requests from a client tend to concentrate on a particular server, causing a poor service response to the client""s request. Therefore, various technology has been proposed in the prior art involving various kinds of traffic control and dispersion of the load on the server. The following literature are related as examples.
A technology is known in Japanese Patent Laid-open No. 9-319689 for selecting an alternate server from a list of candidates servers distributed previously to the client from the name server, when a fault occurs on the server. This technology however becomes expensive since a special process must be provided to the client for selecting the server. This technology has the further drawback of only dealing with load on the server and fails to take into any account whatsoever the load on the network being used. This technology also requires that a fixed substitute server be prepared which drives up the cost still further.
A technology is disclosed in Japanese Patent Laid-open No. 7-154399 for revealing a feedback technology for controlling the data flow amount to the network by utilizing a window for regulating data to a buffer size capable of being transmitted and received on the network. This feedback technology helps avoid congestion however a physical and logically fixed position for client and server is required so that overall network resources are not used efficiently.
A technology is also disclosed in Japanese Patent Laid-open No. 7-319835 for dispersing the load on the server by dispersing files according to the frequency at which a file possessed by a server is accessed. This technology fails to take into account dispersion of the load on the network.
In the technology disclosed in Japanese Patent Laid-open No. 9-244979, re-distribution of service resources is performed based on the frequency of server access and fails to take the load on the network and the congestion status into any account whatsoever. In this technology, re-distribution of service resources requires that the client be aware of the destination address and make the necessary changes.
In the technology disclosed in Japanese Patent Laid-open No. 10-023074, the server is switched when a problem occurs on the server and absolutely no consideration is given to occasions when the network load has increased. Also, this server switching cannot be accomplished unless the server to be switched to is known and unless the required data and applications exist on this next server to be selected. Further, under the precondition that the server of the spare system operate when the server of the currently used system is down, the unique address of the current system server must be handed over to the spare system server so that the server of the currently used system cannot be utilized once switching to the spare server has been performed. In other words, creating the problems that service cannot be performed with the unique address after switching servers, or that communication is disabled in order to perform maintenance and management.